1. Field of the Invention
This invention relates to a joint for coupling tubes, especially fluorocarbon resin tubes, for flowing liquid such as pure water and/a general chemical liquid, used in a clean room in a high-density semiconductor chip manufacturing plant.
2. Description of the Prior Art
This kind of joint is disclosed in Japanese Utility Model Laid-Open No. Heisei 4-122882.
The joint has a deformed tube portion which prevents the tube from coming out of the joint. The joint consists of a fluorocarbon resin tube, the cylindrical main body of the joint, a cap nut and a ring member. The fluorocarbon resin tube has different diameter portion, and a collar is formed at the end of a large diameter portion. A ring-shaped groove where the larger end of the fluorocarbon resin tube is inserted is formed from one end to the mid-portion of the cylindrical main body. The cylindrical main body has threads cut on its outer surface. The major portion of the ring member is also inserted into the ring-shaped groove around the larger end of the fluorocarbon resin tube. To fasten the cylindrical main body with the cap nub, the fluorocarbon ring tube is pressed against the collar tight and then said deformed tube portion is formed. The shoulder of the cap nut presses the intermediate portion of the fluorocarbon resin tube against the end of the cylindrical main body and thereby crimped portion is formed.
In this prior art, two heat-treatment processes and much time is required to form the deformed tube portion. Further, some skill is required in the heat treatment because the collar shape becomes contorted and tight clamping is impossible if temperature variations occurs in heat convection.
Further, quick movements are required to rapidly force the large diameter portion into the cylindrical main body before the large diameter portion becomes cool because the crimped portion contracts gradually after the mold is removed.
A well known kind of prior art joint is disclosed in Japanese Utility Model Laid Open No. Showa 62-86489. A tube of this joint has a large diameter portion and a reinforcing member is forced into there. When a cap nut is tightened to press the large diameter portion, accommodated in the nut, against the main body of the joint, the joint can prevent a tube from coming out of the joint.
This prior art joint has no member for clamping the portion where the large diameter portion and a tube are connected to the main body, and so the tube comes out of the joint easily at high temperature and the hermetic performance as the joint is low. Especially when the outer surface of the tube is slippery as a surface of fluorocarbon resin tube, the tube comes out of the joint frequently and the looseness of the cap nut becomes larger over time.
This joint and the disclosed one in said Japanese Utility Model Laid Open No. Heisei 4-122882 have a common problem as follows. Distortion occurs in the main body, the reinforcing member and the tube deform by using under high temperature or long time use and it causes gaps between contact surfaces among the inner surface of the tube and other members. As a consequence, liquid residue or accumulated polishing particulate in the gaps makes the diameter small.
Accordingly, it is an object of the present invention to solve the above-mentioned problems of the prior art. The invention has a tube clamp portion as a hermetic portion formed by clamping tightly a large diameter portion of the tube inserted into the ring-shaped groove of the cylindrical main body of the joint with a cap nut and pressing firmly a crimp portion of the tube formed at the beginning of the large diameter portion against the end of the cylindrical main body with the hook of the cap nut, and a bevel cut at the end of the cylindrical main body prevents liquid residue from building up.
The point of the present invention to accomplish the foregoing and other objects are as follows.